[1.06] Evolving Dynamics of the Supergranular Flow Field

M.L. DeRosa, J.P. Lisle, J. Toomre (University of Colorado)

We study several large (45-degree square) fields of
supergranules for as long as they remain visible on the
solar disk (about 6 days) to characterize the dynamics of
the supergranular flow field and its interaction with
surrounding photospheric magnetic field elements. These flow
fields are determined by applying correlation tracking
methods to time series of mesogranules seen in full-disk
SOI-MDI velocity images. We have shown previously that
mesogranules observed in this way are systematically
advected by the larger scale supergranular flow field in
which they are embedded. Applying correlation tracking
methods to such time series yields the positions of the
supergranular outflows quite well, even for locations close
to disk center.

These long-duration datasets contain several instances where
individual supergranules are recognizable for time scales as
long as 50 hours, though most cells persist for about 25
hours that is often quoted as a supergranular lifetime. Many
supergranule merging and splitting events are observed, as
well as other evolving flow patterns such as lanes of
converging and diverging fluid. By comparing the flow fields
with the corresponding images of magnetic fields, we confirm
the result that small-scale photospheric magnetic field
elements are quickly advected to the intercellular lanes to
form a network between the supergranular outflows. In
addition, we characterize the influence of larger-scale
regions of magnetic flux, such as active regions, on the
flow fields. Furthermore, we have measured even larger-scale
flows by following the motions of the supergranules, but
these flow fields contain a high noise component and are
somewhat difficult to interpret.

This research was supported by NASA through grants NAG
5-8133 and NAG 5-7996, and by NSF through grant ATM-9731676.

The author(s) of this abstract have provided an email address
for comments about the abstract:
derosa@colorado.edu